Interesting question. By "principles," I assume you are referring to his values or morales which dictate how he acts and what he says and does. One of Creon's first speeches directly refers to his "principles," which also explains why he has refused to allow the body of Polynices to receive proper burial. Note what he says:

These are my principles. Never at my hands

will the traitor be honoured above the patriot.

But whoever proves his loyalty to the state--

I'll prize that man in death as well as life.

Of course, herein lies the conflict of the play, as he ignores the "unwritten laws" that Antigone insists must be upheld by giving her brother proper burial. We can therefore infer that Creon's "principles" involve clinging on to power, whatever the cost, and harshly punishing any form of rebellion, even if that brings him into contact with his own family or the Gods. Creon, by clinging firmly to his principles throughout the play, therefore sows the seeds of his own destruction and in the end loses everything. He remains an important lesson for any would be despot about the dangers of authoritarian power.